In the formation of metal substrates for catalytic converters and the like, such as shown in U.S. Pat. Nos. 3,208,131 and 3,770,389, it is conventional to wind a web of metal substrate material around a mandrel which is slotted at one end thereof. The slotted end of the mandrel is engaged by a rotatable drive component, which drives the mandrel to effect wrapping. The mandrel is normally manually installed in the winding station of a machine and the metal foils (plain and corrugated) to be wrapped around the mandrel are attached to the mandrel by spot welds.
While the prior art procedures are generally suitable, for high speed production machines the slotted mandrel is inadequate to withstand the imposed torque created during the winding operation as a result of the drive bit turning in one direction while a reverse force created by foil tension is applied in an opposite direction. Additionally, with such prior art systems if automatic indexing of the mandrel into operative association with the drive bit--as opposed to manual insertion--is practiced, up to 359.degree. of rotation could be provided, while still providing no guarantee of proper indexing.
According to the present invention, a metal substrate--and method of formation thereof--are provided which eliminate the problems present in the prior art for high speed production. The present invention is practised by forming a torx recess in one end of the mandrel. The torx configuration provides a generally star-shaped recess having smooth curved portions extending between the rounded points of the star. This configuration is eminently suitable for high torque use, and because of the numerous indexing points automatic indexing of the mandrel into operative position with a male drive bit may be provided.
The metal substrate according to the present invention comprises an elongated mandrel having first and second ends; a plurality of wrappings of metal substrate material disposed around the mandrel, and including alternate layers of planar metal foil and corrugated metal foil; means for maintaining the wrappings and mandrel integral; a drilled hole in the first end of the mandrel; and a torx recess formed in second end of the mandrel. Preferably the mandrel is headless, the second end having a slight decreasing taper (e.g. 2.degree.) from the mandrel body toward the second end, and is formed of Inconel.
According to the method of the present invention a metal substrate is formed utilizing a winding machine having a male drive bit, the winding machine being completely automatic. An elongated mandrel is provided, having first and second ends, a drilled hole being provided in the first end and a torx recess being provided in the second end. A web of metal substrate material is affixed to the mandrel, the torx recess of the mandrel is automatically indexed into operative engagement with the male drive bit of the winding machine, and the male drive bit is rotated to wrap the web of metal substrate material around the mandrel, while the web of metal substrate material is fed to the mandrel and while maintaining tension on the web of metal substrate material, until a metal substrate of desired size is obtained. The web is cut and the cut-end is attached to an underlying portion of the metal substrate. The mandrel may be automatically fed into a position to be indexed into operative engagement with the male drive bit of the winding machine. The mandrel is formed from an elongated rod by punching a torx recess into the second end of the rod, and removing the head formed during punching by turning the rod on a lathe, or by shearing the head off by moving a cutting die parallel to the direction of elongation of the rod.
It is the primary object of the present invention to provide a metal substrate and method of formation thereof which may be produced in practice with fully automated, high production machinery. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.